Vitamin D is not seen anymore only as a phosphocalcic hormone, but also as having an effect on global health (anti-infective, anti-inflammatory, anti-tumour roles and cardiovascular protection).

The link between vitamin D deficiency and osteomalacia lesions is well-known. In paediatrics, systematic vitamin D supplementation of infants and toddlers, associated with milk enrichment, has allowed an almost total disappearance of rickets. Vitamin D repletion was defined as the minimal concentration that enables the prevention of rickets in children and osteomalacia in adults, that is approximately 8 ng/mL (20 nmol/L). However, in 2010, most of the international experts agreed to set minimal threshold of 25 OH vitamin D serum concentration, higher than the one previously admitted, with a limit of 20 ng/mL (50 nmol/L) to define a vitamin D deficiency and a limit of 30 ng/mL (75 nmol/L) to define vitamin D insufficiency in adults. In the paediatric population, the consensus is less obvious and we consider that a serum concentration of minimum 20 ng/mL is necessary.

A study on more than 200 children from Lyon, followed in the paediatric nephrology unit and having a renal function normal or sub-normal, demonstrated an important prevalence of vitamin D deficiency (75%) in adolescents and pre-adolescents.

Given the new pathophysiological data on pleiotropic role of vitamin D (bone, cardiovascular system, adipose tissue) and given the proportion of French children possibly suffering from vitamin D deficiency, it seems urgent to actualize current recommendations regarding systematic supplementation in vitamin D. This transversal study on 200 healthy children and adolescents will allow to have an overview of vitamin D status in French healthy children and adolescents, studying with non-invasive, safe, reliable and innovative tools, the theoretical targets of vitamin D (bones, cardiovascular system and nutritional status); and then to lay the foundations of therapeutic trials aiming to evaluate the mode of vitamin D supplementation for healthy children and adolescents; while having a cohort for HR-pQCT measurements, that will allow us to have French reference range in a 10-17 year-old population, for this innovative, non-invasive and low radiation exposure technique.

To study the correlation between the results of bone microarchitecture obtained by high-resolution peripheral quantitative computed tomography (HR-pQCT) and vitamin D serum concentration. [ Time Frame: up to 3 months ] [ Designated as safety issue: No ]

The HR-pQCT evaluates bones down to the level of the tiny individual elements that nature configures in a way that makes bones as strong as possible. HR-pQCT measures bone density and quantifies the three dimensional geometry, strength and microarchitecture of bone at the lower arm (radius) and lower leg (tibia).

Secondary Outcome Measures:

Values and standard deviation of 25-OH vitamin D3 plasma concentration concentration in the population studied. [ Time Frame: Once. At inclusion (V1). ] [ Designated as safety issue: No ]

History of treatment with oral corticoids, taken over more than 3 consecutive months

Current treatment with growth hormone, corticoids or anti-calcineurin

Treatment with aspirin or nonsteroidal anti-inflammatory drug within the last three weeks

Treatment with paracetamol within the last week

Chronic pathology with an impact on growth:

Parenteral nutrition

Chronic inflammatory disease (rheumatologic or digestive notably)

System diseases (lupus, granulomatosis, vascularitis)

Renal failure

Diabetes

Serious intercurrent disease (infection, neoplasia)

Ongoing pregnancy

Patient unaffiliated with the French universal healthcare system.

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Please refer to this study by its ClinicalTrials.gov identifier: NCT01832623